textproduct: Rapid City

KEY MESSAGES

- Scattered showers/isolated thunderstorms will move across the region at times tonight and Wednesday, although many areas will also see long dry periods.

- Drying out for the rest of the week, but southwest flow aloft will bring some possibility of showers or thunderstorms.

- Breezy/windy spots through Wednesday.

UPDATE

Issued at 1046 PM MDT Tue Sep 22 2026

Focus of this evening's forecast update was to rework PoPs and QPF (and resultant Wx grids) tonight and Wednesday to capture radar trends and the new suite of high-res guidance. Nothing particularly heavy or widespread is expected, but enough chance of isolated to scattered showers at times to warrant expanded coverage and redistribution of light PoPs. As the low referenced below lifts northeast tomorrow afternoon and a surface front intrudes into the northern CWA, some CAMs are supporting robust convection for a few hours across the northwestern South Dakota plains, with model soundings advertising moderate instability and strong deep-layer shear over 40kts. The HREF wind gust max does produce localized severe wind gusts with these cells, so that will be something to watch tomorrow.

DISCUSSION

(This Evening Through Tuesday) Issued at 156 PM MDT Tue Sep 22 2026

19z surface analysis had high over the Great Lakes with a warm front from central MT into eastern CO. Modestly tight pressure gradient inbetween promoting southeasterly wind gusts into the 30s on the western SD plains this afternoon. Few shra/TS crawling across south-central SD under weak theta-e advection regime. Water vapour loop had upper ridge from TX into eastern WY with upper low near KSLC. Effect of this system main forecast concern.

Tonight/Wednesday, upper low lifts northeast as it opens up over WY/MT. Stronger low level jet develops ahead of it tonight creating weak buoyancy (<1KJ/kg MUCAPE) in modest low level theta-e advection regime. Result will be some shra/TS lifting northeast across the area into Wednesday. Upslope component to low level flow may support some fog in/near Black Hills/adjacent plains overnight. Temperatures will be near guidance as low clouds slowly scour out east of the Black Hills Wednesday afternoon per movement of warm front.

Thursday into early next week, southwest flow aloft will persist with periodic frontal passages/shortwaves/downslope flow. Warming trend expected with ensembles in relatively good agreement for temperatures (5-10F spreads). Each wiggle will bring PoPs, but there will be plenty of dry hours ahead of most folks.

AVIATION

(For the 06Z TAFS Through 06Z Wednesday Night) Issued At 1123 PM MDT Tue Sep 22 2026

MVFR CIGS (occasional IFR) will persist across much of the western South Dakota plains through tonight and Tuesday morning, especially as isolated to scattered showers cross the area closer to (and after) sunrise. These showers will first cross NE WY/SW SD late tonight before lifting NEwrd. VFR conditions are expected Tuesday afternoon.

UNR WATCHES/WARNINGS/ADVISORIES

SD...None. WY...None.